1. Field of the Invention
This invention relates to a collector for an electric machine, and to a method for its production.
2. Description of the Prior Art
Collectors for electric machines consist of radially disposed centrosymmetrically aligned metallic segments (copper bars) which form a cylindrical rotational body and which are insulated from each other and held together by rings. In the case of the so-called V-ring collector, the segments have a dovetailed construction and are held togethr, with interposition of mica insulation, by V-rings which exert an axial pressure. In contrast, the segments of the shrink-ring collector are held together by shrink rings which exert radial forces on the whole stack of segments. In all cases, the latter must be insulated overall against adjacent metal parts. For this purpose, mica and mica products are predominantly used.
In operation, collectors are subjected to very high mechanical and thermal stresses. For this reason, they are in most cases designed as so-called arch-bound collectors. This means that neighboring segments must not be forced apart even at the higher peripheral speeds (over speed) but must still rest against each other under mutual tangential pressure. The calculation and design of these conventional collectors, therefore, requires great care and experience. Their production and their whole technology (heat treatment, seasoning) represents virtually a craftman's art on which very high demands are made. This is associated with the fact that the mica insulation has a tendency to instability. The mica products have no tensile strength whatever perpendicularly to the plane of their layers and only a negligibly low shear strength parallel to this plane. For this reason, they may be subjected only to pressure loads perpendicularly to the plane of their layers. The individual mica flakes have a tendency to become displaced with respect to each othe which can be caused by non-uniform heating (start-up from standstill in the case of traction motors) or mechanical overloading. This can cause individual segments to be irreversibly displaced and lead to operational disturbances.
The preceding clearly shows that the conventional collector is a quite complicated structure which tends to have mechanical instabilities and geometric changes and the whole production technology of which is time-consuming and expensive and is associated with much mechanical skill. The need exists, therefore, to simplify the design and to shorten the production method.
From the art of metal coating, applied primarily in electronics during the production of printed circuits, the direct bonding of metals to ceramic materials in accordance with the so-called eutectic method is known. In this method, a bonding mechanism which is active in the sub-microscopic atomic region is utilized by generating a metal/metal-oxide eutectic, the melting point of which is only just below that of the pure metal. This bonding mechanism, which acts directly and without additional intermediate layers at the metal/ceramic interfaces permits firmly adhesive bonding between the two unequal components (see, for example, J. F. Burgess and C.A. Neugebauer, "The Direct Bonding of Metals to Ceramics by the Gas-Metal Eutectic Method", J. Electrochem. Soc., May 1975, Vol. 122, No. 5; J. F. Burgess, C. A. Neugebauer, G. Flanagan, R. E. Moore, "The Direct Bonding of Metals to Ceramics and Applications in Electronics", General Electric Report No. 75CRD105, May 1975; U.S. Pat. No. 3,766,634; U.S. Pat. No. 3,911,553).